This invention relates to liquid chromatography and, more particularly, to liquid chromatography equipment utilized in analytical semi-preparative and preparative liquid chromatography separation processes. Specifically, the invention is directed to a novel and useful apparatus and method for mixing appropriate solvents prior to introduction of the mixture into a liquid chromatography column.
Liquid chromatography separation processes are routinely utilized for the analysis of the concentrations of components in liquid samples, typically organic compounds. Liquid chromatography involves introducing one or more solvents and injecting a sample into a column.
Liquid chromatography is a versatile analytical technique due, in part, to the large variety of mobile and stationary phases available. Both polar and non-polar samples can be handled, and separations are obtained on the basis of type and number of functional groups, as well as molecular weight.
Instrumentation for liquid chromatography varies greatly. A schematic diagram of a typical liquid chromatograph is shown in FIG. 1.
The reservoirs contain the solvents to be used as the mobile phase, which are filtered at some point before entering the column. The pumps are very important part of a liquid chromatograph since, without high-pressure capability, liquid chromatography is very time consuming. Both mechanical and pneumatic pumps are used. The pumps can be reciprocating mechanical pumps. Alternatively, constant-displacement mechanical pumps and pneumatic pumps have been incorporated into liquid chromatographs for reducing the amplitude of pulsations. Preferably, the solvents are metered to respective ports of the mixing chamber and admixed prior to introduction into the column.
A pressure gage is typically incorporated into the liquid chromatograph for monitoring the column inlet pressure. One of the more common sample introduction systems consists of an injection port into which the sample is introduced by a syringe through a septum. This necessitates the use of a microsyringe capable of withstanding the high pressures in the liquid chromatograph. The column is typically stainless steel, but heavy-walled glass or glass-lined metal columns are also utilized.
The most commonly used liquid chromatography detector is the ultraviolet photometric detector, but differential refractometers and solute transport detectors are also commonly utilized. Spectra are recorded as a function of elution time by a recorder, and a chromatogram is generated for evaluation.
Known pumps utilized in liquid chromatography systems inherently produce a pulsed flow. The purpose of the mixing chamber is not only to mix the solvents, but also to counteract the effects of pulsed, as opposed to continuous, metering of solvents prior to introduction of the mixture into the column. The mixing chamber averages, or integrates, the metered flows of solvent fed to the input ports of the mixing chamber. The mixing chamber can have plural chambers so as to form a multi-stage mixing chamber for improving the integration characteristic of the mixing chamber.
Unfortunately, the configurations of known mixing chambers have several disadvantages. Typically, known mixing chambers are structured so that the ports for the solvents to be mixed communicate with a sealed compartment on the interior of the mixing chamber. A stirring magnet is disposed within the compartment. A motor is axially positioned beneath the compartment, and a permanent magnet is attached to the drive shaft of the motor for magnetic coupling to the stirring magnet. The compartment communicates through a frit filter to the output port of the mixing chamber, which is also typically axially situated with respect to the compartment and motor/drive magnet assembly. In instances of multi-stage mixing chambers, plural compartments separated by frit filters are typically oriented one above the other in axial alignment between the motor/drive magnet assembly and the output port of the mixing chamber.
As a result, the height of the mixing chamber can be substantial, and the mixing chamber becomes a cumbersome piece of equipment. The size and weight of the mixing chamber are exacerbated by the fact that, as more compartments are added in series in the mixing chamber, the size of the permanent magnet needed for producing a sufficient magnetic field to couple with the stirring magnets increases, as does the size of the motor needed for rotating the drive magnet. This situation is aggravated by the fact that a larger motor is required which increases the construction cost of the mixing chamber.
Moreover, all of the magnets in known multistage mixing chambers rotate in the same direction. If the drive magnet does not have a sufficient strength, the magnetic coupling to the upper stage stirring magnets is insufficient for rotating the stirring magnets, and mixing does not occur in these mixing chambers.
Furthermore, known mixing chambers are operated in a high-pressure environment and must therefore be sealed for preventing leakage of the solvents. Known mixing chambers are typically configured so that the output port is integrated into a threaded cap, which is screwed into a threaded bore in the structure which houses the one or more mixing compartments. The lip of the threaded end of the cap is tightened against a hard plastic gasket, such as a KEL-F (registered trademark) gasket, which resides on a shoulder at the end of the threaded bore, to effect a seal in order to prevent escape of liquid. This requires that the cap be tightened by a large wrench to prevent leakage. Unfortunately, when maintenance of the mixing chamber is required, for example, when one or more frit filters must be replaced, a tool must be found to disassemble the mixing chamber in order to access the interior of the mixing chamber, and a substantial torque must be applied to loosen the cap. If the needed tool is not at hand, significant downtime can result.